Auxiliary oil system for geared gas turbine engine

ABSTRACT

A gas turbine engine comprises a fan drive turbine, a fan rotor, and a gear reduction driven by the fan drive turbine to, in turn, drive the gear architecture. A main oil supply system supplies oil to components within the gear reduction, and an auxiliary oil supply system. The auxiliary oil system operates to ensure that the gear reduction will be adequately supplied with lubricant for at least  30  seconds at power should the main oil supply system fail.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/929,150, filed Jan. 20, 2014.

BACKGROUND OF THE INVENTION

This application relates to an auxiliary oil system to supplement a mainoil supply system on a gas turbine engine with a gear drive for a fan.

Gas turbine engines are known and, typically, include a fan deliveringair into a bypass duct as propulsion air and also delivering air into acore engine. The core engine flow passes into a compressor where it iscompressed and then delivered into a combustion section. The compressedair is mixed with fuel and ignited in the combustion section andproducts of this combustion pass downstream over turbine rotors drivingthem to rotate.

Historically, a turbine rotor drove the fan rotor at a single speed.This led to compromise in the desired speed for both the fan rotor andthe turbine rotor. The fan rotor could not rotate unduly fast and, thus,the turbine rotor typically rotated slower than would be desired.

More recently, it has been proposed to include a gear reduction betweena fan drive turbine and the fan rotor. This has allowed the fan torotate at slower speeds and results in many efficiencies.

However, the gear reduction requires adequate lubrication and must belubricated even under extreme flight conditions.

SUMMARY OF THE INVENTION

In a featured embodiment, a gas turbine engine comprises a fan driveturbine, a fan rotor, and a gear reduction driven by the fan driveturbine to, in turn, drive the gear architecture. A main oil supplysystem supplies oil to components within the gear reduction, and anauxiliary oil supply system. The auxiliary oil system operates to ensurethat the gear reduction will be adequately supplied with lubricant forat least 30 seconds at power should the main oil supply system fail.

In another embodiment according to the previous embodiment, the gearreduction includes a sun gear driven by the fan drive turbine to driveintermediate gears that engage a ring gear.

In another embodiment according to any of the previous embodiments, thesun gear, the intermediate gears and the ring gear are enclosed in abearing compartment, which captures oil removed via a scavenge lineconnected to a main oil pump.

In another embodiment according to any of the previous embodiments, themain oil pump has a gutter that directs scavenged oil to a main oiltank.

In another embodiment according to any of the previous embodiments, oilin the main oil tank feeds a main pump pressure stage which thendelivers oil to the gear reduction.

In another embodiment according to any of the previous embodiments, oilfrom the main pump pressure stage passes through a lubrication systemthat includes at least one filter and at least one heat exchanger tocool the oil.

In another embodiment according to any of the previous embodiments, thegear reduction is surrounded by an oil gutter that scavenges oil anddirects it to an auxiliary oil tank.

In another embodiment according to any of the previous embodiments, theauxiliary oil tank has an overflow conduit that allows excess oil tofall to the bottom of the bearing compartment.

In another embodiment according to any of the previous embodiments, theauxiliary oil tank has a tube with holes at a vertically higher locationthereon, such that oil is drawn from the auxiliary oil tank when it isfull or under negative gravity conditions.

In another embodiment according to any of the previous embodiments, thegutter is at least 70% efficient, defined as the volume of oil capturedin the gutter directed to the auxiliary oil tank compared to a volume ofoil that falls out of the gutter and is scavenged by the main scavengepump.

In another embodiment according to any of the previous embodiments, theauxiliary oil supply system includes an auxiliary pump.

In another embodiment according to any of the previous embodiments, thegear reduction drives auxiliary gears which, in turn, drive theauxiliary pump, such that whenever the gear reduction is turning, itdrives the auxiliary pump.

In another embodiment according to any of the previous embodiments, theauxiliary pump draws oil from the bottom of an oil sump and the bottomof the oil sump is at lower elevation than a line leading from the oilsump to the main pump scavenge stage.

In another embodiment according to any of the previous embodiments, theauxiliary pump also draws oil from the auxiliary oil tank.

In another embodiment according to any of the previous embodiments, theoil sump traps residual oil in the bearing compartment, such that oil issupplied to the auxiliary pump under negative gravity conditions as wellas positive gravity conditions.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a gas turbine engine.

FIG. 2 is a schematic of an oil supply system.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 shows an oil supply system 99 for the gear reduction such as gearreduction 48 in the gas turbine engine 20 of FIG. 1. The gear reduction48 includes a sun gear 100 which is driven by a fan drive turbine (suchas turbine 46 of FIG. 1) and engages a plurality of intermediate gears102. In some embodiments, the intermediate gears 102 may be planet gearsof a planetary epicyclic gear system. In other embodiments, theintermediate gears 102 may be star gears of a star epicyclic gearsystem. In some embodiments, the intermediate gears 102, in turn, drivea ring gear 103 which drives a fan drive shaft to, in turn, rotate a fan(such as fan rotor 42). Other planetary gear arrangements would comewithin the scope of this application and the above is merely one examplefor a gear reduction which may be utilized to drive a fan rotor. Forexample, in other embodiments, a planetary gear carrier (not shown)driven by planetary gears may drive the fan shaft.

Oil supply 104 is shown schematically delivering oil to the planet gears102. It should be understood the oil is supplied to other componentssuch as journal pins, bearings, etc. associated with the geararchitecture illustrated in FIG. 2.

Oil is supplied from a line 106 delivered from a main oil supply pump108. A pressure stage of the main oil supply pump 108 receives oil froman oil tank 142. The oil in the oil tank 142 feeds the main pump 108 andis then conditioned in a lubrication system 110 that may contain filtersto clean the oil and heat exchangers to cool the oil, as known. The oilthen passes back to the gear architecture 48 through the line 106.

A bearing compartment 112 surrounds the gear reduction 48. The bearingcompartment 112 has oil removed via a scavenge line 180, which returnsthe oil to a scavenge side 109 of the main pump 108, which, in turn,delivers the oil back to the oil tank 142.

The gear architecture is surrounded by an oil gutter 114, shownschematically, that scavenges oil from the gear architecture and directsit to an auxiliary tank 116. When tank 116 is full, an overflow conduit117 allows excess oil to fall to the bottom of the bearing compartment112. The gutter 114 is at least 70% efficient. This means that up to 30%of the oil falls out of the gutter and is scavenged by the main scavengepump 109 through line 180. The 70% that is captured in the gutter isdirected into the tank 116.

The detail of the oil supply 104, the gutter 114 and the gears generallymay be as shown in U.S. Patent Application 2008/0116010, now U.S. Pat.No. 8,215,454, issued Jul. 10, 2012. The details of those features areincorporated herein by reference. The gear system and, in particular,the intermediate gears 102 drive auxiliary gears 190 and 191 which areshown schematically driving an auxiliary pump 124. Thus, as long as thegears 102 or 103 are being rotated, the gears 190 and 191 will drive theauxiliary pump 124.

The pump 124 draws oil from a sump 126 at a bottom of the compartment112 through a line 128. The sump 126 is at a lower elevation than themain scavenge line 180 and also draws oil from the tank 116 through theline 122. Sump 126 will trap any residual oil in the bearing compartment112.

There are challenges with the auxiliary pump with regard to negativegravity conditions. Further, if there is a break in the main oil supplysystem or windmilling of the engine when the engine is otherwise shutdown, it is desirable for the engine to be able to maintain operationfor at least 30 seconds at power without damage if the main oil line(108/106, etc.) ruptures. This will provide a pilot time to shut theengine down.

It is also desirable to allow the engine to windmill in the air for upto 90 minutes without damage if it is shut down for other reasons thanoil system failure. It is also desirable to allow the engine to windmillindefinitely on the ground with wind speeds below 85 mph or less. Asknown, windmilling refers to a condition where the engine is shut down,however, air being forced into the fan rotates the fan, in turn, causingcomponents to rotate.

Finally, it is desirable to allow an aircraft to fly under negativegravity conditions for at least 20 seconds.

All of these raise challenges with regard to operating the engine andsupplying oil to the gear components.

The arrangement of the components, as described above, allow theseconditions to be met.

The auxiliary pump 124 draws oil from the sump 126. Pump 124 also drawsoil from a line 122. The tank 116 has a tube 118 with holes 120 at avertically higher location, such that oil is only drawn from the tank116 to the line 122 when it is full or under negative gravityconditions. Otherwise, oil is drained from the tank 116 by overflowthrough the conduit 117.

The auxiliary pump 124 supplies oil to the conduit 130 and then to avalve 132. Valve 132 senses a pressure (through line 140) in the mainline 144. If the pressure is acceptable, oil from the line 130 is sentby the valve 132 back to the tank 142 through a line 199. Thus, if thepressure is acceptable, the oil is recycled for reuse during normaloperation. On the other hand, if the pressure on the main line 144 islow, oil is sent into a conduit 200 and then passes into the conduit 106to bypass the main lubrication system and feed the gear reduction 48 toensure that the conditions as described above are met.

The conditions as described above are met in large part, since theauxiliary oil tank 116, and the tube 118, has the holes 120 only at thetop, such that oil is only drawn from the tank 116, through the line 122when it is full, or under negative G conditions. Further, since the sump126 is at a lower elevation than a main scavenge line 180, the auxiliarypump 124 will always be supplied with oil, in both positive and negativeG conditions. Further, the auxiliary pump 124, in combination with thevalve 132, ensure that oil will be supplied in adequate amounts duringthe conditions set forth above.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A gas turbine engine comprising: a fan drive turbine, a fan rotor,and a gear reduction driven by said fan drive turbine to, in turn, drivesaid gear architecture, a main oil supply system for supplying oil tocomponents within said gear reduction, and an auxiliary oil supplysystem; and said auxiliary oil system being operable to ensure that thegear reduction will be adequately supplied with lubricant for at least30 seconds at power should the main oil supply system fail.
 2. The gasturbine engine as set forth in claim 1, wherein said gear reductionincludes a sun gear being driven by said fan drive turbine to driveintermediate gears that engage a ring gear.
 3. The gas turbine engine asset forth in claim 2, wherein said sun gear, said intermediate gears andsaid ring gear are enclosed in a bearing compartment, which captures oilremoved via a scavenge line connected to a main oil pump.
 4. The gasturbine engine as set forth in claim 3, wherein said main oil pump has agutter that directs scavenged oil to a main oil tank.
 5. The gas turbineengine as set forth in claim 4, wherein oil in said main oil tank feedsa main pump pressure stage which then delivers oil to said gearreduction.
 6. The gas turbine engine as set forth in claim 5, whereinoil from said main pump pressure stage passes through a lubricationsystem that includes at least one filter and at least one heat exchangerto cool the oil.
 7. The gas turbine engine as set forth in claim 4,wherein said gear reduction is surrounded by an oil gutter thatscavenges oil and directs it to an auxiliary oil tank.
 8. The gasturbine engine as set forth in claim 7, wherein said auxiliary oil tankhas an overflow conduit that allows excess oil to fall to the bottom ofsaid bearing compartment.
 9. The gas turbine engine as set forth inclaim 8, wherein said auxiliary oil tank has a tube with holes at avertically higher location thereon, such that oil is drawn from saidauxiliary oil tank when it is full or under negative gravity conditions.10. The gas turbine engine as set forth in claim 7, wherein said gutteris at least 70% efficient, defined as the volume of oil captured in saidgutter being directed to said auxiliary oil tank compared to a volume ofoil that falls out of said gutter and is scavenged by said main scavengepump.
 11. The gas turbine engine as set forth in claim 7, wherein saidauxiliary oil supply system includes an auxiliary pump.
 12. The gasturbine engine as set forth in claim 11, wherein said gear reductiondrives auxiliary gears which, in turn, drive said auxiliary pump, suchthat whenever said gear reduction is turning, it drives said auxiliarypump.
 13. The gas turbine engine as set forth in claim 11, wherein saidauxiliary pump draws oil from the bottom of an oil sump and said bottomof said oil sump is at lower elevation than a line leading from said oilsump to said main pump scavenge stage.
 14. The gas turbine engine as setforth in claim 13, wherein said auxiliary pump also draws oil from saidauxiliary oil tank.
 15. The gas turbine engine as set forth in claim 13,wherein said oil sump traps residual oil in said bearing compartment,such that oil is supplied to said auxiliary pump under negative gravityconditions as well as positive gravity conditions.
 16. The gas turbineengine as set forth in claim 15, wherein said auxiliary oil tank has atube with holes at a vertically higher location thereon, such that oilis drawn from said auxiliary oil tank when it is full or under negativegravity conditions.
 17. The gas turbine engine as set forth in claim 16,wherein oil is also drawn from said auxiliary tank when said tank isfull and through overflow through said overflow conduit.
 18. The gasturbine engine as set forth in claim 11, wherein said auxiliary pumpsupplies oil to a conduit and then to a valve, and said valve sensingpressure in a line associated with said main lubricant supply.
 19. Thegas turbine engine as set forth in claim 18, wherein if said sensedpressure is adequate, oil is supplied from said auxiliary pump back intosaid main oil tank.
 20. The gas turbine engine as set forth in claim 19,wherein if the oil pressure associated with said main oil supply systemis below an adequate pressure, oil is sent from said auxiliary pump tosaid gear reduction.
 21. The gas turbine engine as set forth in claim 1,wherein said auxiliary oil system being operable to allow the engine tooperate under windmill conditions in the air for up to 90 minutes. 22.The gas turbine engine as set forth in claim 21, wherein said auxiliaryoil system being operable to operate indefinitely on the ground whenwindmilling with wind speeds below 85 mph or less.
 23. The gas turbineengine as set forth in claim 22, wherein said auxiliary oil system beingoperable to fly with the engine in an aircraft under negative gravityconditions for at least 20 seconds.
 24. The gas turbine engine as setforth in claim 21, wherein said auxiliary oil system being operable tofly with the engine in an aircraft under negative gravity conditions forat least 20 seconds.
 25. The gas turbine engine as set forth in claim 1,wherein said auxiliary oil system being operable to operate indefinitelyon the ground when windmilling with wind speeds below 85 mph or less.26. The gas turbine engine as set forth in claim 1, wherein saidauxiliary oil system being operable to fly with the engine in anaircraft under negative gravity conditions for at least 20 seconds.